1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus each including an electrophotographic photosensitive member.
2. Description of the Related Art
Currently, electrophotographic photosensitive members containing organic photoconductive materials are mainly used as electrophotographic photosensitive members for use in process cartridges and electrophotographic apparatuses. Typically, an electrophotographic photosensitive member includes a support and a photosensitive layer disposed on the support. To inhibit the charge injection from the support side to the photosensitive layer side (charge generating layer) and inhibit the occurrence of image failure, such as fogging, an intermediate layer is provided between the support and the photosensitive layer. To cover a surface defect of the support, it is known that a conductive layer containing metal oxide particles may be provided.
In recent years, charge generating materials with higher sensitivities have been used. A higher sensitivity of a charge generating material results in a larger amount of charges generated. Thus, charges in exposed portions are disadvantageously liable to stay in photosensitive layers when a very large number of the same images are output in a short period of time. As a technique for inhibiting the residence of charges in a photosensitive layer, it is known that a technique in which the incorporation of an electron transporting material into an intermediate layer permits the intermediate layer to have an ability to transport electrons (hereinafter, also referred to as an “electron transporting layer”).
PCT Japanese Translation Patent Publication No. 2009-505156 discloses an electrophotographic photosensitive member including an electron transporting layer that contains a polymer of a crosslinking agent and a condensation polymer (electron transporting material) having a crosslinking site, and an aromatic tetracarbonylbisimide skeleton; and a conductive layer that contains tin oxide particles. Japanese Patent Laid-Open No. 2008-65173 discloses an electrophotographic photosensitive member including a layer that contains an electron acceptor material; and a conductive layer that contains an electron acceptor material and zinc oxide particles whose surfaces are treated with a silane coupling agent.
Japanese Patent Laid-Open Nos. 2007-148294 and 2008-250082 disclose electrophotographic photosensitive members including electron transporting layers on conductive layers that contain titanium oxide particles coated with tin oxide.
In recent years, electrophotographic images have been required to have better image quality. The number of opportunities to output a very large number of the same images in a short period of time has been increased.
The results of studies by the inventors demonstrated that in that case, image failure what is called pattern memory is liable to occur. The term “pattern memory” refers to a phenomenon in which when a solid black image 302 is output after a large number of images 301 each containing vertical lines 306 in FIG. 3 are continuously output, the output solid black image is an image 304 containing vertical lines 307 due to the repetitive hysteresis of the vertical lines 306 in the images 301 illustrated in FIG. 3. When a halftone image 303 is output after a large number of the images 301 are continuously output, the term “pattern memory” refers to a phenomenon in which the halftone image is an image 305 containing vertical lines 308 due to the repetitive hysteresis of the vertical lines 306 in the images 301 illustrated in FIG. 3, as with the solid black image.
It was found than in the electrophotographic photosensitive members including the conductive layers and the electron transporting layer or the electron acceptor material-containing layer described in PCT Japanese Translation Patent Publication No. 2009-505156 and Japanese Patent Laid-Open No. 2008-65173, charges are liable to stay between each of the conductive layers and a corresponding one of the electron transporting layers, so that the foregoing pattern memory occurs, in some cases.
To inhibit the retention of charges between the conductive layer and the electron transporting layer, it is conceivable that the electrical resistance is reduced by increasing the content of metal oxide particles in the conductive layer. However, it was found that the reduction in the electrical resistance of the conductive layer leads to insufficient adhesion of the electron transporting layer and thus that the application of a high voltage is liable to cause leakage to occur in the electrophotographic photosensitive member. The term “leakage” refers to a phenomenon in which dielectric breakdown occurs in a local portion of an electrophotographic photosensitive member, and excessive current flows therethrough. The occurrence of the leakage can cause image failure, for example, a black spot or a horizontal black line, because the electrophotographic photosensitive member is not sufficiently charged.